Motion artifact detection and correction

ABSTRACT

An apparatus and method are provided for motion artifact detection and correction, where an apparatus includes a scanning device for receiving two-dimensional image slices of an object, a rendering device in signal communication with the scanning device for rendering a three-dimensional volume representation of the two-dimensional image slices, and a correction device in signal communication with the rendering device for correcting motion artifacts within the three-dimensional volume representation; and a corresponding method for detecting motion artifacts within scan data of a region comprising an object includes creating a three-dimensional representation with volume elements of the region based on the scan data, analyzing the volume elements along a boundary of the object, and determining the existence of a motion artifact in response to the analyzing.

CROSS-REFERENCE

[0001] This application claims the benefit of U.S. Provisional PatentApplication Serial No. 60/331,714, entitled “CT Movement DetectionMethod” and filed Nov. 21, 2001, which is incorporated herein byreference in its entirety.

BACKGROUND

[0002] The present disclosure relates to volume based three-dimensionalvirtual examinations, and more particularly relates to a system andmethod for detection and correction of motion artifacts introducedduring scanning.

[0003] Two-dimensional (“2D”) visualization of human organs usingmedical imaging devices has been widely used for patient diagnosis.Currently available medical imaging devices include computed tomography(“CT”) and magnetic resonance imaging (“MRI”), for example.Three-dimensional (“3D”) images can be formed by stacking andinterpolating between two-dimensional pictures produced from thescanning machines. Imaging an organ and visualizing its volume inthree-dimensional space would be beneficial due to the lack of physicalintrusion and the ease of data manipulation. However, the exploration ofthe three-dimensional volume image must be properly performed in orderto fully exploit the advantages of virtually viewing an organ from theinside.

[0004] Although the scanning speeds of modern MRI, CT scanners and likeequipment are an improvement over earlier technologies, they generallyremain slow enough that patient movement during a scan can causeblurring of a boundary formed by the tissue of the patient and thebackground of the scanning equipment. This blurring is usually referredto as “motion artifact”. Accordingly, it is desirable to provide ascanning system and method capable of detecting and correcting thesemotion artifacts.

SUMMARY

[0005] These and other drawbacks and disadvantages of the prior art areaddressed by a system and method for motion artifact detection andcorrection. An apparatus and method are provided for motion artifactdetection and correction, where an apparatus includes a scanning devicefor receiving two-dimensional image slices of an object, a renderingdevice in signal communication with the scanning device for rendering athree-dimensional volume representation of the two-dimensional imageslices, and a correction device in signal communication with therendering device for correcting motion artifacts within thethree-dimensional volume representation.

[0006] A corresponding method for detecting motion artifacts within scandata of a region comprising an object includes creating athree-dimensional representation with volume elements of the regionbased on the scan data, analyzing the volume elements along a boundaryof the object, and determining the existence of a motion artifact inresponse to the analyzing.

[0007] Accordingly, an aspect of the present disclosure relates to amethod for detecting motion artifacts within scan data of a regionincluding an object from a radiological scanning device. According tothis aspect, a three-dimensional representation of the region based onthe scan data is created. From among the volume elements of thethree-dimensional representation, the one or more volume elements alonga boundary of the object are analyzed to determine if one or more motionartifacts exist within the three-dimensional representation. Anexemplary region would be the field of view of a CT scanning device withan exemplary object being a patient's abdomen. Motion artifacts caninclude both breathing motion and body-shift.

[0008] These and other aspects, features and advantages of the presentdisclosure will become apparent from the following description ofexemplary embodiments, which is to be read in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Further objects, features and advantages of the presentdisclosure will become more apparent from the following detaileddescription of preferred embodiments, taken in conjunction with theaccompanying Figures, in which:

[0010]FIG. 1 shows a flow chart of the steps for performing a virtualexamination of an object, specifically a colon, in accordance with thedisclosure;

[0011]FIG. 2 shows an illustration of a “submarine” camera model whichperforms guided navigation in the virtual organ;

[0012]FIG. 3 shows a diagram illustrating a two dimensionalcross-section of a volumetric colon which contains the flight path;

[0013]FIG. 4 shows a diagram of a system used to perform a virtualexamination of a human organ in accordance with the disclosure;

[0014]FIG. 5 illustrates imaginary planes used to define exemplaryboundary profiles according to an embodiment of the present invention;

[0015]FIG. 6 illustrates exemplary profiles that depict the presence orabsence of motion artifacts;

[0016]FIG. 7 illustrates motion artifact regions in a boundary profilethat can be corrected according to an embodiment of the presentinvention;

[0017]FIG. 8 depicts a flowchart for detecting and correcting motionartifacts according to an embodiment of the present invention; and

[0018]FIG. 9 shows a block diagram of a system embodiment based on apersonal computer bus architecture.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0019] A system and method are provided for generating athree-dimensional (“3D”) visualization image of an object, such as anorgan, using volume visualization techniques, where the resultingvisualization is suitable for use with a guided navigational system. Aguided navigational system allows the operator to travel along a flightpath and to adjust the view to a particular portion of the image ofinterest in order, for example, to identify polyps, cysts or otherabnormal features in the visualized organ. One or more bisectingprofiles are acquired along the sagittal and corollary plane. Theseprofiles are then analyzed to determine whether a patient has movedduring the scan. Additionally, the profiles can be used to estimate theamount of patient movement and thereby enable corresponding correctionof the scan data to remove any false artifacts resulting from themovement.

[0020] While the methods and systems described herein may be applied toany object to be examined, preferred embodiments include the examinationof an organ in the human body, such as the colon, for example. The colonis long and twisted, which makes it especially suited for a virtualexamination, saving the patient the money, discomfort and danger of aphysical probe. Other examples of organs or systems that can bevirtually examined include the lungs, stomach and portions of thegastrointestinal system, and the heart and blood vessels.

[0021] As shown in FIG. 1, a method for performing a virtual examinationof an object such as a colon is indicated generally by the referencenumeral 100. The method 100 illustrates the steps necessary to perform avirtual colonoscopy using volume visualization techniques. Step 101prepares the colon to be scanned in order to be viewed for examinationif required by either the doctor or the particular scanning instrument.This preparation could include cleansing the colon with a “cocktail” orliquid, which enters the colon after being orally ingested and passedthrough the stomach. The cocktail forces the patient to expel wastematerial that is present in the colon. One example of a substance usedis Golytcly. Additionally, in the case of the colon, air or carbondioxide can be forced into the colon in order to expand it to make thecolon easier to scan and examine. This is accomplished with a small tubeplaced in the rectum with approximately 1,000 cc of air pumped into thecolon to distend the colon. Depending upon the type of scanner used, itmay be necessary for the patient to drink a contrast substance such asbarium to coat any unexpunged stool in order to distinguish the waste inthe colon from the colon walls themselves. Alternatively, the method forvirtually examining the colon can remove the virtual waste prior to orduring the virtual examination as explained later in this specification.Step 101 does not need to be performed in all examinations as indicatedby the dashed line in FIG. 1.

[0022] Step 103 scans the organ that is to be examined. The scanner canbe an apparatus well known in the art, such as a spiral CT-scanner forscanning a colon or a Zenith MRI machine for scanning a lung labeledwith xenon gas, for example. The scanner must be able to take multipleimages from different positions around the body during suspendedrespiration, in order to produce the data necessary for the volumeVisualization. For example, data can be acquired using a GE/CTI spiralmode scanner operating in a helical mode of 5 mm, 1.5-2.0:1 pitch,reconstructed in 1 mm slices, where the pitch is adjusted based upon thepatient's height in a known manner. A routine imaging protocol of 120kVp and 200-280 ma can be utilized for this operation. The data can beacquired and reconstructed as 1 mm thick slice images having an arraysize of 512×512 pixels in the field of view, which varies from 34 to 40cm depending on the patient's size. The number of such slices generallyvaries under these conditions from 300 to 450, depending on thepatient's height. The image data set is converted to volume elements orvoxels.

[0023] An example of a single CT-image would use an X-ray beam of 5 mmwidth, 1:1 to 2:1 pitch, with a 40 cm field-of-view being performed fromthe top of the splenic flexure of the colon to the rectum.

[0024] Discrete data representations of the object can be produced byother methods besides scanning. Voxel data representing an object can bederived from a geometric model by techniques described in U.S. Pat. No.5,038,302 entitled “Method of Connecting Continuous Three-DimensionalGeometrical Representations into Discrete Three-Dimensional Voxel-BasedRepresentations Within a Three-Dimensional Voxel-Based System” byKaufman, issued Aug. 8, 1991, filed Jul. 26, 1988, which is herebyincorporated by reference in its entirety. Additionally, data can beproduced by a computer model of an image, which can be converted tothree-dimensional voxels and explored in accordance with thisdisclosure.

[0025] Step 104 converts the scanned images into three-dimensionalvolume elements (“voxels”). In a preferred embodiment for examining acolon, the scan data is reformatted into 5 mm thick slices at incrementsof 1 mm or 2.5 mm and reconstructed in 1 mm slices, with each slicerepresented as a matrix of 512 by 512 pixels. By doing this, voxels ofapproximately 1 cubic mm are created. Thus a large number of 2D slicesare generated depending upon the length of the scan. The set of 2Dslices is then reconstructed to 3D voxels. The conversion process of 2Dimages from the scanner into 3D voxels can either be performed by thescanning machine itself or by a separate machine such as a computerimplementing techniques that are well known in the art (see, e.g., U.S.Pat. No. 4,985,856 entitled “Method and Apparatus for Storing,Accessing, and Processing Voxel-based Data” by Kaufman et al.; issuedJan. 15, 1991, filed Nov. 11, 1988; which is hereby incorporated byreference in its entirety).

[0026] Step 105 allows the operator to define the portion of theselected organ to be examined. A physician may be interested in aparticular section of the colon likely to develop polyps. The physiciancan view a two dimensional slice overview map to indicate the section tobe examined. A starting point and finishing point of a path to be viewedcan be indicated by the physician/operator. A conventional computer andcomputer interface (e.g., keyboard, mouse or spaceball) can be used todesignate the portion of the colon that is to be inspected. A gridsystem with coordinates can be used for keyboard entry or thephysician/operator can “click” on the desired points. The entire imageof the colon can also be viewed if desired.

[0027] Step 107 performs the planned or guided navigation operation ofthe virtual organ being examined. Performing a guided navigationoperation is defined as navigating through an environment along apredefined or automatically predetermined flight path, which can bemanually adjusted by an operator at any time. After the scan data hasbeen converted to 3D voxels, the inside of the organ is traversed fromthe selected start to the selected finishing point. The virtualexamination is modeled on having a tiny viewpoint or “camera” travelingthrough the virtual space with a view direction or “lens” pointingtowards the finishing point. The guided navigation technique provides alevel of interaction with the camera, so that the camera can navigatethrough a virtual environment automatically in the case of no operatorinteraction, and at the same time, allow the operator to manipulate thecamera when necessary. The preferred embodiment of achieving guidednavigation is to use a physically based camera model that employspotential fields to control the movement of the camera, as is furtherdetailed with respect to FIGS. 2 and 3.

[0028] Step 109, which can be performed concurrently with step 107,displays the inside of the organ from the viewpoint of the camera modelalong the selected pathway of the guided navigation operation.Three-dimensional displays can be generated using techniques well knownin the art such as the marching cubes technique, for example. In orderto produce a real time display of the colon, a technique is used thatreduces the vast number of data computations necessary for the displayof the virtual organ.

[0029] The method described in FIG. 1 may also be applied to scanningmultiple organs in a body at the same time. For example, a patient maybe examined for cancerous growths in both the colon and lungs. Themethod of FIG. 1 would be modified to scan all the areas of interest instep 103 and to select the current organ to be examined in step 105. Forexample the physician/operator may initially select the colon tovirtually explore and later explore the lung. Alternatively, twodifferent doctors with different specialties may virtually exploredifferent scanned organs relating to their respective specialties.Following step 109, the next organ to be examined is selected and itsportion will be defined and explored. This continues until all organsthat need examination have been processed.

[0030] The steps described in conjunction with FIG. 1 may also beapplied to the exploration of any object that can be represented byvolume elements. For example, an architectural structure or inanimateobject can be represented and explored in the same manner.

[0031] Turning to FIG. 2, a “submarine camera” model that performsguided navigation in a virtual organ is indicated generally by thereference numeral 200. The model 200 depicts a viewpoint control modelthat performs the guided navigation technique of step 107. When there isno operator control during guided navigation, the default navigation issimilar to that of planned navigation that automatically directs thecamera along a flight path from one selected end of the colon toanother. During the planned navigation phase, the camera stays at thecenter of the colon for obtaining better views of the colonic surface.When an interesting region is encountered, the operator of the virtualcamera using guided navigation can interactively bring the camera closeto a specific region and direct the motion and angle of the camera tostudy the interesting area in detail, without unwillingly colliding withthe walls of the colon. The operator can control the camera with astandard interface device such as a keyboard, mouse or nonstandarddevice such as a spaceball. In order to fully operate a camera in avirtual environment, six degrees of freedom for the camera are required.The camera must be able to move in the horizontal, vertical, and depthor Z direction (axes 217), as well as being able to rotate in anotherthree degrees of freedom (axes 219) to allow the camera to move and scanall sides and angles of a virtual environment.

[0032] Methods for computing a centerline inside the area of interestare well known in the art (see, e.g., U.S. Pat. No. 5,971,767 entitled“SYSTEM AND METHOD FOR PERFORMING A THREE-DIMENSIONAL VIRTUALEXAMINATION” by Kaufman et al.; issued Oct. 26, 1999 and incorporated byreference herein in its entirety).

[0033] Referring to FIG. 3, a two dimensional cross-section of avolumetric colon containing a flight path is indicated generally by thereference numeral 300. The cross-section 300 includes the final flightpath for the camera model down the center of the colon, as indicated by“x”s, and at least one starting location 301 or 303 near one end of thecolon.

[0034] Turning now to FIG. 4, a system used to perform a virtualexamination of a human organ in accordance with the disclosure isindicated generally by the reference numeral 400. The system 400 is forperforming the virtual examination of an object such as a human organusing the techniques described herein. A patient 401 lays on a platform402, while a scanning device 405 scans the area that contains the organor organs to be examined. The scanning device 405 contains a scanningportion 403 that takes images of the patient and an electronics portion406. The electronics portion 406 includes an interface 407, a centralprocessing unit 409, a memory 411 for temporarily storing the scanningdata, and a second interface 413 for sending data to a virtualnavigation platform or terminal 416. The interfaces 407 and 413 may beincluded in a single interface component or may be the same component.The components in the portion 406 are connected together withconventional connectors.

[0035] In the system 400, the data provided from the scanning portion403 of the device 405 is transferred to unit 409 for processing and isstored in memory 411. The central processing unit 409 converts thescanned 2D data to 3D voxel data and stores the results in anotherportion of the memory 411. Alternatively, the converted data may bedirectly sent to the interface unit 413 to be transferred to the virtualnavigation terminal 416. The conversion of the 2D data could also takeplace at the virtual navigation terminal 416 after being transmittedfrom the interface 413. In the preferred embodiment, the converted datais transmitted over a carrier 414 to the virtual navigation terminal 416in order for an operator to perform the virtual examination. The datamay also be transported in other conventional ways, such as storing thedata on a storage medium and physically transporting it to terminal 416or by using satellite transmissions, for example.

[0036] The scanned data need not be converted to its 3D representationuntil the visualization-rendering engine requires it to be in 3D form.This saves computational steps and memory storage space.

[0037] The virtual navigation terminal 416 includes a screen for viewingthe virtual organ or other scanned image, an electronics portion 415 andan interface control 419 such as a keyboard, mouse or spaceball. Theelectronics portion 415 includes an interface port 421, a centralprocessing unit 423, optional components 427 for running the terminaland a memory 425. The components in the terminal 416 are connectedtogether with conventional connectors. The converted voxel data isreceived in the interface port 421 and stored in the memory 425. Thecentral processing unit 423 then assembles the 3D voxels into a virtualrepresentation and runs the submarine camera model as described in FIGS.2 and 3 to perform the virtual examination. As the submarine cameratravels through the virtual organ, the visibility technique as describedin FIG. 9 is used to compute only those areas that are visible from thevirtual camera, and displays them on the screen 417. A graphicsaccelerator can also be used in generating the representations. Theoperator can use the interface device 419 to indicate which portion ofthe scanned body is desired to be explored. The interface device 419 canfurther be used to control and move the submarine camera as desired asdetailed for FIG. 2. The terminal portion 415 can be, for example, theCube-4 dedicated system box, generally available from the Department ofComputer Science at the State University of New York at Stony Brook.

[0038] The scanning device 405 and terminal 416, or parts thereof, canbe part of the same unit. A single platform would be used to receive thescan image data, connect it to 3D voxels if necessary and perform theguided navigation.

[0039] An important feature in system 400 is that the virtual organ canbe examined at a later time without the presence of the patient.Additionally, the virtual examination could take place while the patientis being scanned. The scan data can also be sent to multiple terminals,which would allow more than one doctor to view the inside of the organsimultaneously. Thus a doctor in New York could be looking at the sameportion of a patient's organ at the same time with a doctor inCalifornia while discussing the case. Alternatively, the data can beviewed at different times. Two or more doctors could perform their ownexamination of the same data in a difficult case. Multiple virtualnavigation terminals could be used to view the same scan data. Byreproducing the organ as a virtual organ with a discrete set of data,there are a multitude of benefits in areas such as accuracy, cost andpossible data manipulations.

[0040] Some of the applicable techniques may be further enhanced invirtual colonoscopy applications through the use of a number ofadditional techniques that are described in U.S. Pat. No. 6,343,936entitled “SYSTEM AND METHOD FOR PERFORMING A THREE-DIMENSIONAL VIRTUALEXAMINATION, NAVIGATION AND VISUALIZATION” by Kaufman et al.; issuedFeb. 7, 2002, which is incorporated herein by reference in its entirety.These improvements, described briefly below, include improved coloncleansing, volume rendering, additional fly-path determinationtechniques, and alternative hardware embodiments.

[0041] An improved electronic colon cleansing technique employs modifiedbowel preparation operations followed by image segmentation operations,such that fluid and stool remaining in the colon during a computedtomographic (“CT”) or magnetic resonance imaging (“MRI”) scan can bedetected and removed from the virtual colonoscopy images. Through theuse of such techniques, conventional physical washing of the colon, andits associated inconvenience and discomfort, is minimized or completelyavoided.

[0042] In addition to image segmentation and texture mapping,volume-rendering techniques may be used in connection with virtualcolonoscopy procedures to further enhance the fidelity of the resultingimage. Methods for volume rendering are well known to those of ordinaryskill in the pertinent art.

[0043] As shown in FIG. 5, a plot of imaginary planes used to defineexemplary boundary profiles is indicated generally by the referencenumeral 500. The plot 500, for example, depicts four imaginary planesthat intersect a patient's body. There are two sagittal planes SP1 andSP2 and there are two corollary planes CP1 and CP2. Each of these planesintersects the boundary 504 of the patient's body and, at thisintersection, creates a profile that can be analyzed. The sagittalprofiles are more sensitive to breathing motion or superior-posteriormovement of the abdomen, while the corollary profiles are more sensitiveto body shift. Thus, in the exemplary embodiment of FIG. 5, fourprofiles are created using the four planes SP1, SP2, CP1, CP2.

[0044] The SP1 and SP2 planes each create a profile that has a topregion distant from the table 502 and a bottom region proximate thetable 502. As the table 502 is assumed not to move, and the patient'smovement against the table 502 is minimal, only the top region of eachof the sagittal profiles is analyzed. The corollary profiles have a leftregion and a right region representing the left and right sides of thepatient's body. According to one embodiment of the present invention,one corollary profile (e.g., from CP1) is used to analyze the leftboundary while the other corollary profile (e.g., from CP2) is used toanalyze the right boundary.

[0045] Turning to FIG. 6, a plot of exemplary profiles that depict thepresence or absence of motion artifacts is indicated generally by thereference numeral 600. The plot 600 illustrates exemplary profilescreated from an intersecting sagittal plane. The frame on the left 602shows breath motion visible in the abdomen contour 604; while the frameon the right 608 shows no motion artifact.

[0046] Turning now to FIG. 7, a plot of correctable motion artifactregions in a boundary profile is indicated generally by the referencenumeral 700. The plot 700 illustrates an exemplary method for correctingfor motion artifacts. In this figure, a smooth abdomen curve 702 is fitto the top of the abdomen profile 708 that shows breathing motion. Theimaginary abdomen curve 702 is considered “smooth” because it iscalculated to have a roughness measure less than the predeterminedthreshold. The vertical lines 704 and 706 in FIG. 7 represent axialplanes that intersect the abdomen profile or contour 708. These axialplanes correspond to two-dimensional scan images that were acquiredduring scanning of the patient. Correction for motion artifacts isperformed by comparing each axial plane in the scanned profile 708 withthe calculated smooth contour 702 and then adjusting the pixel data ineach axial plane based on the comparison. More particularly, for eachaxial plane, the difference between the smooth curve 702 and the actualabdomen boundary 708 is utilized to adjust the axial plane to remove themotion artifact. The adjustment can be done using conventional imagemanipulation and transformation techniques to accomplish stretching,shifting, shrinking or some other transformation.

[0047] For example, the left vertical line 704 represents an axial planethat needs to be transformed upwards to match with the smooth abdomencurve 702. The right vertical line 706 represents an axial plane thatwould need to be transformed downwards to align with the smooth abdomencurve 702.

[0048] In the example of FIG. 7, since the scan is of the abdomen andthe patient is lying on a fixed table, an interpolation in the verticaldirection (for all pixels in the axial plane) can be performed in whichthe bottom of the plane is not transformed at all while the top of theplane is adjusted so that the boundary 708 aligns with the smooth curve702. Between these two points, the adjustment percent can beinterpolated between “no transformation” at the bottom and the “fullamount” required at the top. This interpolation can be linear, somehigher order, or some continuous smooth operation. Alternatively, in anexample without the fixed table, the transformation of the axial planecould include nearly zero adjustment at the center of the axial planeand substantially similar stretching (or shrinking) at top and bottomedges of the axial plane. Additionally, the interpolation can even takeinto account the density of the CT scan to adjust the amount of possiblestretching or shrinking possible for a particular axial plane.

[0049] Once the axial planes have been corrected, the volume elementscan be recalculated using the corrected scan data. While an example ofonly a sagittal boundary for an abdomen scan has been explicitlyprovided, embodiments of the present invention contemplate detecting andcorrecting for motion artifacts related to other regions and objects ofa patient and other plane profiles (e.g., corollary).

[0050] Referring to FIG. 8, a method for detecting and correcting motionartifacts is indicated generally by the reference numeral 800. Themethod 800 is for detecting and correcting motion artifacts according toan embodiment of the present invention. According to the flowchart, thefirst steps are the initial steps of performing any scan such as, forexample, for a virtual colonoscopy or other virtual examination. In step802, the patient is prepared for the scan in a manner appropriate forthe scanning technology. Next, in step 804, the patient is scanned toacquire the multiple individual two-dimensional slices of the region, orobject, of interest. For example, the scan could be a CT scan of theabdomen for the purposes of performing a virtual colonoscopy. Next, instep 806, the scan data is converted into volume elements according toconventional methods described previously.

[0051] Once the volume elements are available for analysis, they can beused to help detect if a motion artifact exists within the scan data. Instep 808, one or more virtual planes are defined which intersect thepatient and the object of interest.

[0052] For each profile, the contour of the body's boundary 504 can beobtained by conventional thresholding techniques applied, in step 810,to the volume data intersected by the plane (e.g., SP1, SP2, CP1, CP2)used to create the profile. The body's boundary 504 usually has a sharpintensity slope compared to the background of the scan and, thus, eachprofile can be readily determined. If necessary, more advancedregion-growing techniques can be employed to remove the background anddelineate the body contour. After obtaining each profile or contour, theroughness of the profile is measured in step 812. If the boundary of anobject is smooth, such as a patient's body contour 504, then the profileof the boundary of CT images should also be smooth. When the boundary,however, is blurred such as by movement of the patient, then the profileis no longer smooth. By detecting the roughness of the boundary profile,the existence of motion artifacts in CT images, and other scanningtechnologies, can be detected. One exemplary measurement of roughness isto use first order derivatives. According to this exemplary method, thefirst order derivatives are calculated along the profile. Specifically,for each unit step in the horizontal direction, the change in thevertical direction is determined along the profile. If the amplitude(either positive or negative) of the first order derivative is greaterthan a predetermined threshold, then a motion artifact is detected.

[0053] There are other alternatives to first-order derivativemeasurements, such as, for example, fractal-based roughnessmeasurements. Also, the pre-set threshold depends on the feature beinganalyzed, the scale of the images, and the scan technology being used.It is an empirical value that is application driven.

[0054] In step 812, the roughness is calculated individually for eachprofile. If there is at least one profile in which the roughness islarger than the pre-set threshold, then patient movement during the scanis detected. Knowing that movement occurred can prevent wasting time andeffort analyzing data that includes a motion artifact. In addition, oralternatively, the motion artifact can be corrected for, in step 814.

[0055] Detecting and Correcting for Movement in CT Scanning

[0056] Turning to FIG. 9, a system embodiment based on a personalcomputer bus architecture is indicated generally by the referencenumeral 900. The system 900 includes an alternate hardware embodimentsuitable for deployment on a personal computer (“PC”), as illustrated.The system 900 includes a processor 910 that preferably takes the formof a high speed, multitasking processor, such as, for example, a PentiumIII processor operating at a clock speed in excess of 400 MHZ. Theprocessor 910 is coupled to a conventional bus structure 920 thatprovides for high-speed parallel data transfer. Also coupled to the busstructure 920 are a main memory 930, a graphics board 940, and a volumerendering board 950. The graphics board 940 is preferably one that canperform texture mapping, such as, for example, a Diamond Viper v770Ultra board manufactured by Diamond Multimedia Systems. The volumerendering board 950 can take the form of the VolumePro board fromMitsubishi Electric, for example, which is based on U.S. Pat. Nos.5,760,781 and 5,847,711, which are hereby incorporated by reference intheir entirety. A display device 945, such as a conventional SVGA or RGBmonitor, is operably coupled to the graphics board 940 for displayingthe image data. A scanner interface board 960 is also provided forreceiving data from an imaging scanner, such as an MRI or CT scanner,for example, and transmitting such data to the bus structure 920. Thescanner interface board 960 may be an application specific interfaceproduct for a selected imaging scanner or can take the form of ageneral-purpose input/output card. The PC based system 900 willgenerally include an I/O interface 970 for coupling I/O devices 980,such as a keyboard, digital pointer or mouse, and the like, to theprocessor 910. Alternatively, the I/O interface can be coupled to theprocessor 910 via the bus 920.

[0057] Embodiments of the present disclosure provide a user interfacedisplaying both two-dimensional and three-dimensional data. Organswithin the body are, by nature, three-dimensional. Conventional medicalimaging devices, however, as explained herein, create stacks oftwo-dimensional images when acquiring scan data. Radiologists and otherspecialists, therefore, have historically been trained to review andanalyze these two-dimensional images. As a result, most doctors arecomfortable viewing two-dimensional images even if three-dimensionalreconstructions or virtualizations are available.

[0058] However, many organs are not simple convex objects but, instead,can be tortuous or have many branches. While a doctor may be comfortableanalyzing two-dimensional images, performing navigation through complexorgans is very difficult using merely two-dimensional images. Navigatingusing the two-dimensional images would include manually scrollingthrough the images to move in the “z” direction (along the major axis ofthe body) and panning the images to move in the “x” and “y” direction.In this manner an operator can traverse the organ looking for areas ofinterest.

[0059] On the other hand, three-dimensional flight paths, as describedherein, are intuitive, efficient tools to virtually travel throughvolumetric renderings of human organs either automatically or manually.During a flight path tour, each point along the flight path isrepresented by a coordinate (x, y, z). According to embodiments of thepresent disclosure, these coordinates are used to automatically scrolland pan the series of two-dimensional images that doctors are used toanalyzing. Thus, the operator does not have to manually navigate throughan organ in two dimensions but, instead, can let the presentvirtualization system advance along the organ while the operatorconcentrates on analyzing each two-dimensional image.

[0060] Although the scanning speed of modern MRI and other suchequipment is a vast improvement over earlier technologies, it remainsslow enough that patient movement during a scan can cause blurring ofboundary formed by the tissue of the patient and the background of thescanning equipment. This blurring is usually referred to as “motionartifact”. Thus, a scanning system and method that can detect andcorrect for motion artifacts has been disclosed herein.

[0061] In the exemplary environment of abdominal CT scans, the causes ofmotion artifacts include breathing, body rotation and body shifts.Breathing usually causes the superior-posterior movement of the abdomenand body shift causes left-right movement of the body.

[0062] Embodiments of the present invention use a virtual plane tobisect the scanned object (e.g., a patient's abdomen) to get a profileof the boundary of that object. The smoothness or roughness of theboundary between the object's profile and the background is measured andused to determine whether a motion artifact exists in the CT data orother types of images.

[0063] The foregoing merely illustrates the principles of thedisclosure. It will thus be appreciated that those skilled in the artwill be able to devise numerous systems, apparatus and methods which,although not explicitly shown or described herein, embody the principlesof the disclosure and are thus within the spirit and scope of thedisclosure as defined by its claims.

[0064] For example, the methods and systems described herein could beapplied to virtually examine an animal, fish or inanimate object.Besides the stated uses in the medical field, applications of thetechnique could be used to detect the contents of sealed objects thatcannot be opened. The technique could also be used inside anarchitectural structure such as a building or cavern and enable theoperator to navigate through the structure.

[0065] These and other features and advantages of the present disclosuremay be readily ascertained by one of ordinary skill in the pertinent artbased on the teachings herein. It is to be understood that the teachingsof the present disclosure may be implemented in various forms ofhardware, software, firmware, special purpose processors, orcombinations thereof.

[0066] Most preferably, the teachings of the present disclosure areimplemented as a combination of hardware and software. Moreover, thesoftware is preferably implemented as an application program tangiblyembodied on a program storage unit. The application program may beuploaded to, and executed by, a machine comprising any suitablearchitecture. Preferably, the machine is implemented on a computerplatform having hardware such as one or more central processing units(“CPU”), a random access memory (“RAM”), and input/output (“I/O”)interfaces. The computer platform may also include an operating systemand microinstruction code. The various processes and functions describedherein may be either part of the microinstruction code or part of theapplication program, or any combination thereof, which may be executedby a CPU. In addition, various other peripheral units may be connectedto the computer platform such as an additional data storage unit and aprinting unit.

[0067] It is to be further understood that, because some of theconstituent system components and methods depicted in the accompanyingdrawings are preferably implemented in software, the actual connectionsbetween the system components or the process function blocks may differdepending upon the manner in which embodiments of the present disclosureare programmed. Given the teachings herein, one of ordinary skill in thepertinent art will be able to contemplate these and similarimplementations or configurations of the present invention.

[0068] Although the illustrative embodiments have been described hereinwith reference to the accompanying drawings, it is to be understood thatthe present invention is not limited to those precise embodiments, andthat various changes and modifications may be effected therein by one ofordinary skill in the pertinent art without departing from the scope orspirit of the present disclosure. All such changes and modifications areintended to be included within the scope of the present invention as setforth in the appended claims.

What is claimed is:
 1. A method for detecting motion artifacts withinscan data of a region comprising an object, the method comprising:creating a three-dimensional representation comprising volume elementsof the region based on the scan data; analyzing a plurality of thevolume elements along a boundary of the object; and determining theexistence of at least one motion artifact in response to the analyzing.2. A method as defined in claim 1, further comprising correcting thescan data to remove the at least one motion artifact.
 3. A method asdefined in claim 1 wherein analyzing comprises: determining a contour ofa boundary of the object within the three-dimensional representation;measuring a roughness of the contour; and determining that a motionartifact exists if the roughness of the contour exceeds a predeterminedthreshold.
 4. A method as defined in claim 3, further comprising:repeating, for each of a plurality of boundaries of the object, thesteps of determining a contour and measuring a roughness; anddetermining that a motion artifact exists if the roughness of anycontour exceeds a predetermined threshold.
 5. A method as defined inclaim 1 wherein analyzing comprises: defining a plane intersecting aboundary of the object within the three-dimensional representation ofthe region; identifying a contour of the boundary coinciding with thedefined plane; measuring a roughness of the identified contour; anddetermining that a motion artifact exists if the measured roughness ofthe identified contour exceeds a predetermined threshold.
 6. A method asdefined in claim 5, further comprising: repeating, for each of aplurality of planes, the steps of defining a plane, identifying acontour and measuring a roughness; and determining that a motionartifact exists if the roughness of the identified contour exceeds apredetermined threshold.
 7. A method as defined in claim 6 wherein theplurality of planes comprises a first pair of parallel planes and asecond pair of parallel planes, said second pair orthogonal to saidfirst pair.
 8. A method as defined in claim 1 wherein the at least onemotion artifact reflects motion of the object in at least one of thevertical and horizontal directions.
 9. A method as defined in claim 5wherein the step of identifying a contour of the boundary is performedusing thresholding techniques to distinguish the object from a regionbackground.
 10. A method as defined in claim 5 wherein the step ofmeasuring roughness comprises calculating a magnitude of the firstderivative at intervals along the contour.
 11. A method as defined inclaim 5 wherein the step of correcting comprises: calculating a smoothcontour based on the identified contour; and transforming the identifiedcontour to align with the smooth contour.
 12. A method as defined inclaim 11, further comprising: identifying one or more regions of theidentified contour that do not align with the smooth contour, each ofsaid regions having an associated axial plane orthogonally intersectingthe defined plane; for each such identified region, calculating arespective transformation to align the identified contour with thesmooth contour; and correcting the scan data within each said axialplane according to the respective transformation.
 13. A method asdefined in claim 1 wherein said scan data is from a radiologicalscanning device.
 14. A method as defined in claim 1 wherein said objectis disposed in a human abdomen.
 15. A method as defined in claim 14,further comprising: intersecting the three-dimensional representationwith a corollary plane, thereby creating a first profile of the abdomenwithin a background of the field of view; and intersecting thethree-dimensional representation with a sagittal plane, thereby creatinga second profile of the abdomen within a background of the field ofview.
 16. A method as defined in claim 15, further comprising:thresholding the first profile to identify a corollary contour of theabdomen; and thresholding the second profile to identify a sagittalcontour of the abdomen.
 17. A method as defined in claim 16 wherein thesagittal contour reveals any breathing motion of the abdomen and thecorollary contour reveals any body-shift of the abdomen.
 18. A method asdefined in claim 16, further comprising: calculating a first roughnessmeasure of the corollary contour; calculating a second roughness measureof the sagittal contour; and determining that a motion artifact existsif either roughness measure exceeds a respective threshold.
 19. A methodas defined in claim 18 wherein each of the first and second roughnessmeasures is calculated, at points corresponding to each of the axialplanes representing slices of the abdomen, by calculating the magnitudeof the first derivative along the respective contour.
 20. A method asdefined in claim 19, further comprising: calculating a smooth sagittalcontour; identifying a set of points on the sagittal contour that do notalign with the smooth sagittal contour; determining at a plurality ofpoints of the set of points a respective transformation to align thesagittal contour with the smooth sagittal contour; and for the axialplane corresponding to the plurality of points of the set of points,transforming scan data within that axial plane based on the determinedrespective transformation.
 21. A method as defined in claim 19, furthercomprising: calculating a smooth corollary contour; identifying a set ofpoints on the corollary contour that do not align with the smoothcorollary contour; determining at a plurality of points of the set ofpoints a respective transformation to align the corollary contour withthe smooth corollary contour; and for the axial plane corresponding tothe plurality of points of the set of points, transforming scan datawithin that axial plane based on the determined respectivetransformation.
 22. A method for performing a three-dimensional virtualexamination of at least one object, the method comprising: scanning witha scanning device to produce scan data representative of said object;creating a three-dimensional volume representation of said objectcomprising volume elements from said scan data; and correcting for oneor more motion artifacts within said three-dimensional volumerepresentation.
 23. A method as defined in claim 22 wherein said objectis elongated, the method further comprising: selecting at least one endvolume element from about one end of said corrected three-dimensionalvolume representation; generating a defined path from said end volumeelement extending to about the other end of said correctedthree-dimensional volume representation; performing a guided navigationof said corrected three-dimensional representation along said path; anddisplaying in real time said volume elements responsive to said path.24. A method as defined in claim 23 wherein said displayed volumeelements are further responsive to an operator's input during saidguided navigation.
 25. A method as defined in claim 22 whereincorrecting for one or more motion artifacts comprises: detecting the oneor more motion artifacts within the three-dimensional volumerepresentation; editing the scan data based on the detected one or moremotion artifacts; and creating a corrected three-dimensional volumerepresentation of said object from the edited scan data.
 26. A method asdefined in claim 22 wherein the object is an organ within a body.
 27. Amethod as defined in claim 26 wherein the organ is a colon.
 28. A methodas defined in claim 26 wherein the organ is a lung.
 29. A method asdefined in claim 26 wherein the organ is a heart.
 30. A program storagedevice readable by machine, tangibly embodying a program of instructionsexecutable by the machine to perform method steps for detecting motionartifacts within scan data of a region comprising an object, the stepscomprising: creating a three-dimensional representation comprisingvolume elements of the region based on the scan data; analyzing aplurality of the volume elements along a boundary of the object; anddetermining the existence of at least one motion artifact in response tothe analyzing.
 31. A program storage device as defined in claim 30, thesteps further comprising correcting the scan data to remove the at leastone motion artifact.
 32. A program storage device as defined in claim30, the steps for analyzing comprising: determining a contour of aboundary of the object within the three-dimensional representation;measuring a roughness of the contour; and determining that a motionartifact exists if the roughness of the contour exceeds a predeterminedthreshold.
 33. An apparatus for performing a three-dimensional virtualexamination of at least one object, the apparatus comprising: scanningmeans for scanning with a scanning device and producing scan datarepresentative of said object, said scan data comprising a sequence oftwo-dimensional images of said object; volume-rendering means forcreating a three-dimensional volume representation of said objectcomprising volume elements from said scan data; and correction means forcorrecting for one or more motion artifacts within saidthree-dimensional volume representation.
 34. An apparatus as defined inclaim 33, further comprising: selection means for selecting at least oneend volume element from said three-dimensional volume representation;flight-path means for generating a defined path including said endvolume element along said three-dimensional volume representation;navigational means for performing a guided navigation of saidthree-dimensional representation along said path; and display means fordisplaying in real time said volume elements responsive to said path andto an operator's input during said guided navigation and simultaneouslydisplaying at least one of the sequence of two-dimensional images basedon a current location along the defined path.
 35. An apparatus forperforming a three-dimensional virtual examination of at least oneobject, the apparatus comprising: a scanning device for receiving aplurality of two-dimensional image slices of at least one object; arendering device in signal communication with the scanning device forrendering a three-dimensional volume representation of the plurality oftwo-dimensional image slices; and a correction device in signalcommunication with the rendering device for correcting for one or moremotion artifacts within said three-dimensional volume representation.36. An apparatus as defined in claim 35, further comprising: aprocessing device in signal communication with the correction device forlocating a first set of features along a centerline within the renderedthree-dimensional volume representation; an indexing device in signalcommunication with the processing device for matching at least onefeature in the rendered three-dimensional volume representation with acorresponding two-dimensional image slice; and a display device insignal communication with the indexing device for displaying both of therendered three-dimensional volume representation and the matchedtwo-dimensional image slice.